1. Field of the Invention
The present invention relates generally to the field of systems for diagnosing, treating, and monitoring sleep disorders. More specifically, the present invention discloses a system for monitoring and treating sleep disorders, such as sleep apnea and hypopnea, using a transtracheal catheter.
2. Statement of the Problem
The conventional approach to diagnosis of sleep disorders has been to require the patient to participate in a "sleep study". The patient is outfitted with an array of sensors attached to the surface of the body to monitor the patient's respiration, pulse, and blood oxygen saturation. A strip chart recorder traces the sensor signals on paper for later analysis by a health care professional.
Conventional sleep studies have several shortcomings. The complexity and expense of the required equipment dictate that sleep studies are usually conducted in a clinic setting, i.e., a hospital or sleep laboratory. This significantly increases the costs involved. In addition, the patient often finds it difficult to sleep in a strange setting, particularly while wearing sensors tethered by wires to a strip chart recorder. Respiration is typically measured by requiring the patient to wear sensor devices applied to the face and body, which is especially uncomfortable to wear while trying to sleep.
With newer technology, sleep studies can be done in the home, but this still involves attaching various sensor devices and wires to the body surface. These tests are usually single night events, and are too complex and expensive to be practical in monitoring treatment efficacy and patient compliance over extended periods of time, such as days, weeks, or months.
The most common treatment of sleep apnea involves the uncomfortable sensation of blowing air under pressure into the upper airway via a mask strapped to the face. Continuous positive airway pressure (CPAP) and bi-level positive airway pressure (BiPAP) are the treatment modalities that have been delivered by masks. Even though sleep apnea is often corrected with CPAP and BiPAP, both have excessively high non-compliance rates due patient discomfort.
Therefore, a clear need exists for a respiration monitoring system for diagnosis of sleep disorders that is suitable for use outside of clinical settings, and minimizes patient discomfort. This system has even greater value if administered in conjunction with transtracheal augmentation of ventilation, which offers greater efficacy, comfort, and compliance over existing technology, such as BiPAP and CPAP.
3. Prior Art
The prior art relevant to the present invention falls into several different categories:
Transtracheal Catheters
Transtracheal catheters have been used for several years to deliver a flow of air/oxygen into the patient's trachea and lungs to supplement the patient's spontaneous respiration. Transtracheal oxygen therapy is commonly used to support patients with compromised respiratory systems, such as resulting from emphysema or chronic obstructive respiratory disease (COPD), and pulmonary fibrosis.
Spofford et al. (U.S. Pat. Nos. 5,186,168 and 5,090,408) disclose a system for continuously supplying supplemental oxygen to a patient through a transtracheal catheter at relatively low pressures and relatively low flow rates.
Christopher (U.S. Pat. Nos. 5,279,288 and 5,419,314) discloses a system for augmenting ventilation of a spontaneously-breathing patient using a transtracheal catheter. A high continuous flow of humidified air/oxygen is supplied through a transtracheal catheter into the patient's trachea and lungs. Clinical experience indicates that transtracheal augmentation of ventilation is efficacious and more comfortable than previous technology using BiPAP or CPAP. Compliance appears to improve as well. Christopher mentions that the system can be used to treat sleep apnea. The increased tracheal pressure produced by the high flow of air/oxygen helps to keep the patient's upper airway open and thereby reduces the frequency and severity of episodes of sleep apnea and hypopnea.
Leger et al. (French Patent No. 2594034) discloses a first embodiment of a transtracheal catheter with a single lumen in FIGS. 1-3. A gate mechanism 6 measures the back pressure through the catheter and uses this information to control the flow rate 13 to match the patient's inspiration as shown in FIGS. 4 and 5. The second embodiment shown in cross-section in FIG. 8 has two lumens. The second lumen 23 carries a low flow of oxygen at a pressure slightly higher than atmospheric pressure, as shown by the dashed line P23 in FIG. 9. The back pressure, PM, measured through the second lumen is used to control the flow rate 13 through the gate mechanism 6 as shown in FIGS. 9 and 10. In particular, the gate 6 opens whenever PM passes downward through P23 (indicating the start of inspiration), and closes whenever PM passes upward through P23.
Pressure Sensors
The prior art also includes a wide variety of systems for monitoring respiration or detecting sleep apnea using pressure transducers. For example:
Sander et al. (U.S. Pat. No. 5,148,802) disclose a system for maintaining airway patency to treat sleep apnea by alternating high and low level positive airway pressure through a face mask. The high and low airway pressure are coordinated with the patient's spontaneous respiration. This is an example of a BiPAP system.
Fry (U.S. Pat. No. 4,459,982) discloses servo-controlled demand regulator for a respiratory ventilator. Gas is supplied through an endotracheal tube 34 to coincide with the patient's respiratory pattern as monitored by a pressure transducer.
Brady et al. (U.S. Pat. No. 5,385,142) discloses an apnea-sensitive ventilator that measures both pressure and flow.
Essen-Moller (U.S. Pat. No. 5,477,860) discloses a multi-lumen catheter for measuring respiration using an external pressure transducer connected to one of the lumens. The patient's respiration is monitored and recorded.
Sackner (U.S. Pat. Nos. 4,648,407 and 4,860,766) discloses a method for monitoring intrapleural pressure in newborns. The system includes a pressure transducer connected to a strip chart recorder, and a thermistor placed under the patient's nostrils for measuring flow.
Bacaner et al. (U.S. Pat. No. 4,966,141) and Broadhurst et al. (U.S. Pat. No. 5,043,576) disclose an endotracheal tube that can also be used for mass spectrometry. The endotracheal tube has multiple lumens for measuring pressure and flow rate, and for gas sampling.
Bombeck (U.S. Pat. No. 4,981,470) discloses an intraesophageal catheter with a pH sensor. The catheter also includes a pressure sensor for monitoring sleep apnea.
Pfohl (U.S. Pat. No. 4,981,139) discloses a system for monitoring vital signs that includes an esophageal stethoscope 14 with a pressure transducer.
Flow Sensors
The prior art includes a number of references that employ a thermistor or other flow sensor for measuring the patient's breathing rate or flow rate, e.g., Bacaner et al. (U.S. Pat. No. 4,966,141), Broadhurst et al. (U.S. Pat. No. 4,850,371), and Sackner (U.S. Pat. Nos. 4,648,407 and 4,860,766). However, none of these involve a transtracheal catheter.
Wilkinson (U.S. Pat. No. 5,413,111) and Stasz (U.S. Pat. No. 5,311,875) cover breathing sensors for diagnosing sleep apnea that are placed under the nostrils.
Wittmaier et al. (U.S. Pat. No. 4,366,821) disclose a breathing monitor having an endotracheal tube with a thermistor 14 (FIG. 2) to measure the patient's breathing rate.
Oximeters
The prior art includes many references that disclose general examples of optical oximetry, such as Mendelson et al. (U.S. Pat. No. 5,277,181), Fatt (U.S. Pat. No. 3,893,444), Shaw et al. (U.S. Pat. Nos. 3,847,483, 4,114,604, and 4,416,285), Sperinde (U.S. Pat. No. 4,623,248), and Sperinde et al. (U.S. Pat. No. 4,453,218). Several of the prior art references combine various types of catheters with an oximeter, e.g., Robinson et al. (U.S. Pat. No. 5,494,032), Johnson (U.S. Pat. No. 3,866,599), and Moran et al. (U.S. Pat. No. 4,776,340). Buchanan (U.S. Pat. No. 5,005,573) shows an endotracheal tube with an oximeter. Brain (U.S. Pat. No. 5,282,464) discloses a reflectance oximeter 23 mounted on the upstream side of a laryngeal mask to face the posterior wall of the pharynx.
4. Solution to the Problem
None of the prior art references discussed above show a system for both monitoring patient respiration patterns and supplying a supplemental continuous flow of air/oxygen through a transtracheal catheter for diagnosis, treatment, and monitoring of sleep disorders, such as sleep apnea. In particular, none of the prior art references discussed above show the combination of a multi-lumen transtracheal catheter, a pressure transducer, and means for recording the patient's breathing patterns over time. The transtracheal catheter in the present system can also be equipped with a flow sensor, oximeter, or capnometer to generate more complete data for diagnosis.
The present system overcomes a number of disadvantages associated with conventional sleep studies by eliminating the need for external sensors attached to the body and permitting data to be gathered conveniently while the patient remains at home. In addition, the present system can be readily installed as an add-on to conventional transtracheal augmented ventilation therapy. In this configuration, the system can be used to record respiration data for an initial diagnosis, and subsequently used on an ongoing basis for monitor the effectiveness of transtracheal augmented ventilation therapy in treating sleep disorders, such as obstructive sleep apnea and hypopnea.